Turbocharger with a shaft comprising a free portion

ABSTRACT

A turbocharger includes a compressor and a compressor housing (1) surrounding the compressor, a turbine and a turbine housing (2) surrounding the turbine. The compressor housing (1) includes an inlet and an outlet for the air (4) entering a combustion chamber of an engine. The turbine housing (2) includes an inlet and an outlet for the exhaust gases (5), a shaft (3) linking the turbine and the compressor, at least one bearing for supporting and guiding the rotation of the shaft (3). The turbocharger includes attachment means (6, 7a, 7b) for attaching the turbine housing (2) to the compressor housing (1). The shaft (3) includes a free portion (8) between the two housings (1, 2), the attachment means (6, 7a, 7b) being suitable for allowing the passage of a flow of air circulating along the free portion (8) and around the turbine housing (2) and compressor housing (1).

FIELD OF THE INVENTION

The invention relates to a turbocharger, in particular a turbocharger for an internal combustion engine.

DESCRIPTION OF THE PRIOR ART

The turbocharger is a forced induction system very widely used in internal combustion engines for the purpose of increasing the power of these engines. The principle is to increase the density of the air supplied to the combustion chamber of the engine by compressing it using a compressor that is connected by a shaft to a turbine which is in turn set in rotation by the exhaust gases. For optimal operation, a turbocharger generally requires the use, downstream of the turbocharger, of a heat exchanger in order to cool the air and thus further increase its density, since compressed air generally has an elevated temperature at the outlet of the turbocharger. Owing to their high temperature, the exhaust gases constitute the main source of heat within the turbocharger. Thus, these exhaust gases drive an increase in temperature which is non-beneficial both for the air compressed by the turbocharger and also for the bearings of the shaft connecting the compressor and the turbine.

Document US2014/0352299 discloses a turbocharger in which a cooling duct is designed so as to convey part of the air compressed in the compressor close to the bearing of the shaft between the turbine and the compressor. A cooling system of this kind therefore has the aim of cooling the bearing in order to protect it from the heating due to the friction of the shaft in the bearing and due to the high temperatures of the exhaust gases.

Document US2012/0003081 also discloses a turbocharger in which a cooling jacket is designed to bring compressed air directly from the compressor or downstream thereof into a cavity for the purpose of cooling the bearing of the shaft. A passage, which may or may not contain an overpressure valve, is therefore provided between the interior of the compressor casing and the cooling cavity.

Thus, the above-mentioned turbochargers of the prior art make use of the air admitted into the compressor for the purpose of cooling the bearing or bearings supporting the shaft that connects the turbine to the compressor. However, the above-mentioned systems do not make it possible to reduce the negative impact of the flow of heat generated by the turbine inlet gases on the air admitted to the compressor.

SUMMARY OF THE INVENTION

The present invention is defined in the appended independent claim. The preferred embodiments are defined in the dependent claims.

According to a first aspect, the present invention relates to a turbocharger comprising a compressor and a compressor casing that encloses said compressor, a turbine and a turbine casing that encloses said turbine, said compressor casing comprising an inlet and an outlet for the air admitted to a combustion chamber of an engine, said turbine casing comprising an inlet and an outlet for the exhaust gases, a shaft connecting said turbine and said compressor, at least one bearing for supporting and guiding in rotation said shaft, said turbocharger comprising means for securing the compressor casing to the turbine casing, said shaft comprising a free portion between the two casings, said securing means being suitable for permitting the passage of a flow of air flowing along said free portion and around said compressor casing and turbine casing.

The presence of the free portion, which is therefore a portion of the shaft connecting the compressor to the turbine which is not enclosed within a bearing housing, makes it possible to reduce the conduction of heat, from the turbine casing to the compressor casing, which is conventionally observed in the prior art. Indeed, it has been observed that the presence of a bearing housing surrounding all of that portion of the shaft between the compressor casing and the turbine casing gave rise to a non-negligible flow of heat from the turbine casing, which is therefore heated by the exhaust gases, to the compressor casing, in which any increase in temperature is therefore disadvantageous owing to the resulting decrease in density of the compressed air.

Thus, the free portion of the shaft communicates directly with the exterior of the turbocharger since the means for securing the compressor casing to the turbine casing allow a flow of outside air to pass around said casings and along said free portion, with direct contact between the flow of air and the free portion. Thus, and in contrast to that observed in the prior art, the presence of this free portion substantially decreases the transfers of heat by thermal conduction between the two casings.

According to one advantageous embodiment, the means for securing the compressor casing to the turbine casing comprise a plurality of bars.

According to one advantageous embodiment, the turbocharger comprises two bearing housings for supporting the shaft connecting the compressor to the turbine, the first bearing housing being located between the turbine casing and the free portion of the shaft, the second bearing housing being located between the compressor casing and the free portion of the shaft. The first bearing housing is secured to the turbine casing and the second bearing housing is secured to the compressor casing. Thus, the first and second bearing housings support in rotation the shaft connecting the compressor to the turbine, and may contain any type of bearing suitable for fulfilling this function, whether they are, for example, journal bearings or rolling-element bearings. The first and second bearing housings advantageously comprise an inlet and an outlet for receiving a lubricant, and seals for preventing leakage of lubricant toward the free portion of the shaft and the turbine and compressor casings.

According to one advantageous embodiment, the free portion of the shaft comprises air deflection means, said air deflection means being suitable for generating a flow of air when said shaft is rotating. Very advantageously, the air deflection means are suitable for generating a flow of air flowing in the direction from the compressor casing to the turbine casing. Indeed, a flow of air flowing in that direction permits optimal ventilation of the compressor casing, drawing around the latter a flow of air at ambient temperature coming from outside the turbocharger, while blowing away the hot air that surrounds the turbine casing, and consequently preventing this hot air from heating the compressor casing. The presence of, on one hand, the free portion on the shaft connecting the compressor to the turbine and, on the other hand, air deflection means that generate a flow of air from the compressor casing toward the turbine casing along the free portion thus permits optimal cooling of the compressor casing while reducing the thermal conduction between the compressor casing and the turbine casing, and furthermore effecting efficient ventilation of the air close to the compressor casing. This ensures optimal thermal insulation of the compressor casing with respect to the turbine casing. With such a system, it can be observed that the efficiency of the engine connected to the turbocharger is significantly improved, and also that it is no longer necessary to use an intercooler. In other embodiments, the ventilation can be brought about, either entirely or in addition to the above-described ventilation system, by ventilation means located outside the turbocharger and supplied with energy by an external energy source. For example, said air ventilation means may comprise a fan located close to the compressor casing.

According to one advantageous embodiment, the air deflection means comprise a plurality of blades, for example two blades, which are attached to the free portion of the shaft and will therefore be made to rotate when the turbocharger is powered by the exhaust gases.

According to one advantageous embodiment, the turbocharger according to the invention comprises a protective shell that surrounds the free portion of the shaft connecting the turbine to the compressor. A shell of this kind acts as a protective barrier for the free portion of the shaft, which will have a very high rotational speed during operation of the turbocharger. A shell of this kind may also cover all of the compressor and turbine casings, while leaving openings around the compressor and turbine casings in order to allow the passage of the flow of air generated by the air deflection means that are advantageously present on the free portion of the shaft. In this case, the shell then acts as a barrier to prevent direct contact between an operator and the casings, in particular the turbine casing which will have a high temperature during operation. The protective shell may be secured to the means for securing the turbine casing to the compressor casing, or directly to the turbine and compressor casings.

According to a second aspect, the invention relates to a vehicle, comprising an internal combustion engine connected to a turbocharger as described above. Moreover, a plurality of turbochargers according to the invention may be installed on a single vehicle, being mounted in series or in parallel, for the purpose of optimizing the forced induction performance in the various operating ranges of the engine. Furthermore, in a vehicle comprising a turbocharger according to the invention and a catalytic converter in its exhaust line for the purpose of reducing the toxicity of the exhaust gases, the turbine casing of the turbocharger may advantageously be connected to the exhaust gases of the engine downstream of the catalytic converter. Indeed, the exhaust gases are at a lower temperature at the outlet of the catalytic converter than at the inlet of the latter, and it has therefore been observed that such a configuration was consequently advantageous for the purpose of minimizing transfers of heat to the compressor casing, and thus optimizing the performance of the turbocharger.

BRIEF DESCRIPTION OF THE FIGURES

These aspects of the invention, and other complementary aspects, will be explained in greater detail by means of examples and with reference to the appended drawing:

FIG. 1 shows an embodiment of the turbocharger according to the invention;

FIG. 2 shows an embodiment of a protective shell that can be used with the turbocharger according to the invention.

The figures are not drawn to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the turbocharger according to the invention. Thus, the turbocharger consists of a compressor casing 1 that houses a radial compressor, and of a turbine casing 2 that houses a radial turbine. The turbine is connected to the compressor by a shaft 3. Thus, the compressor draws in the air 4 that is intended to be admitted to the engine and, once it has compressed this air, thus sends it to the intake duct of the engine. The turbine, for its part, is driven by the exhaust gases 5 from the engine. The compressor casing 1 is secured to the turbine casing 2 via the intermediary of a plurality of bars 6 and attachment plates 7 a and 7 b secured to said casings 1 and 2. The shaft 3 comprises a free portion 8 between the two casings 1 and 2.

Thus, the free portion 8 communicates with the exterior of the turbocharger. In particular, the bars 6 allow the passage of a flow of air coming from the exterior of the turbocharger and flowing around the two casings 1 and 2 and along the free portion 8, with the bars 6 allowing direct contact between the flow of air and the free portion 8. The presence of this free portion 8 greatly reduces the transfers of heat by thermal conduction, from the turbine casing to the compressor casing, which are observed in the prior art when a central bearing housing is inserted between the two casings and is in contact therewith.

The shaft 3 is advantageously supported by two bearings located in bearing housings 9 a and 9 b. The bearing housing 9 a is secured to the compressor casing via the intermediary of the attachment plate 7 a, while the bearing housing 9 b is secured to the turbine casing via the intermediary of the attachment plate 7 b. The bearings housed in the bearing housings 9 a and 9 b may be of any kind provided that they are capable of fulfilling their role, specifically supporting and guiding in rotation the shaft 3. The bearings may be, for example, journal bearings, rolling-element bearings or foil bearings. Moreover, since the proper operation of a bearing generally requires a supply of lubricant, inlets and outlets (not shown) for draining lubricant are advantageously created in the bearing housings 9 a and 9 b. To avoid lubricant leaking toward the free portion 8 and the compressor and turbine casings 1 and 2, seals (not shown) are advantageously introduced into the bearing housings 9 a and 9 b. Moreover, when a lubricating oil conveyed to the bearings of the turbocharger is first used to lubricate other elements of the internal combustion engine, it is advantageous to provide a cooling system, such as a heat exchanger, in the lubricating oil distribution circuit upstream of the turbocharger, in order to minimize the temperature of this lubricating oil at the point at which it enters the turbocharger. Moreover, it is important to mention that the presence of two bearing housings is not strictly necessary. It is also possible to envisage embodiments in which a single bearing housing is present. The only bearing housing may be the housing 9 a or 9 b, or a bearing housing placed at a more intermediate position between the two casings 1 and 2.

The free portion 8 of the shaft 3 of the turbocharger shown in FIG. 1 comprises two blades 10 that form a helix around the shaft 3. Thus, these blades constitute air deflection means actuated in rotation and capable of generating a flow of air 11 along the free portion 8 when the turbocharger is driven by the exhaust gases 5. The geometry of the blades 10 (not shown) is chosen so as to generate a flow of air going from the compressor casing to the turbine casing when the turbine and the compressor are driven in rotation. Indeed, a flow of air flowing in that direction permits optimal ventilation of the compressor casing 1, drawing around the latter a flow of air at ambient temperature coming from outside the turbocharger, while blowing away the hot air that surrounds the turbine casing 2, and consequently preventing this hot air from heating the compressor casing 1. Thus, in the system according to the invention, the shaft connecting the compressor to the turbine has a new role which is to serve as a rotating support for a fan that draws a flow of air around the compressor casing 1. The presence of, on one hand, the free portion 8 on the shaft 3 and, on the other hand, air deflection means that generate a flow of air from the compressor casing 1 toward the turbine casing 2 along the free portion 8 thus permits optimal cooling of the compressor casing 1 while reducing the thermal conduction between the compressor casing 1 and the turbine casing 2, and furthermore effecting efficient ventilation of the air close to the compressor casing 1. With such a system, it can be observed that the efficiency of the engine connected to the turbocharger is significantly improved, and also that it is no longer necessary to use an intercooler.

The turbocharger shown in FIG. 1 advantageously comprises a protective shell 12, which in this instance is depicted as transparent for greater clarity, although an opaque shell could of course be used. A shell 12 of this kind serves to protect access to the free portion 8 of the shaft 3, and in particular to the blades 10 attached to the shaft 3, which will rotate at very high speed during operation of the turbocharger. When it covers the compressor casing 1 and turbine casing 2, the shell 12 then also acts as a barrier to prevent direct contact between an operator and the casings, in particular the turbine casing which will have a very high temperature during operation. The protective shell 12 may be secured to the bars 6 for securing the turbine casing to the compressor casing, or may be secured directly to the turbine and compressor casings, via the intermediary of attachment means such as struts 13. However, the protective shell 12 leaves openings around the compressor casing 1 and turbine casing 2 to allow the passage of the flow of air 11. The air 11 evacuated around the turbine casing 2 may also be recovered by a heat recovery system and serve to heat certain components or regions of the vehicle.

Moreover, the turbocharger according to the invention may be a variable-geometry turbocharger, that is to say provided with a turbine that is able to regulate the flow of the exhaust gases, thereby adjusting the flow rate in order to optimize the power of the turbine in dependence on the required load. Furthermore, the turbocharger according to the invention may comprise a plurality of compressors and/or turbines arranged in sequence. The turbocharger may for example comprise a central turbine connected to two compressors, one on either side of the turbine. A free portion 8 around which a flow of air is able to flow is then advantageously included on the shaft between the turbine and each of the two compressors.

FIG. 2 shows in greater detail an embodiment of the shell 12 which can be used with the turbocharger according to the invention. This shell 12 advantageously comprises a part 14 for at least partially surrounding the compressor casing 1 and a part 15 for at least partially surrounding the turbine casing 2. These two parts 14 and 15 advantageously meet in a central region in order to surround the shaft 3 of the turbocharger, and are connected by securing means such as securing rods 16. Part 14 is advantageously a tubular part comprising an inlet opening 14 a for the flow of air 11, and an outlet opening 14 b for the egress of this flow of air 11. Part 14 advantageously comprises a frustoconical portion 17. The frustoconical portion 17 is advantageously located between a distal small-diameter cylindrical portion 18 and a proximal large-diameter cylindrical portion 19. Part 15, surrounding the turbine casing 2, is advantageously also a tubular part comprising an inlet hole 20 into which is inserted the distal portion 18 of part 14. The securing means 16 advantageously comprise 4 rods that are connected to the frustoconical portion 17 of part 14, and to the walls of the inlet hole 20 of part 15. Advantageously, part 15 also comprises an outlet hole 21 for the egress of the flow of air 11. The distal portion 18 is advantageously inserted into the inlet hole 20 of part 15 with no contact therewith. Indeed, the presence of a space between the distal portion 18 and the walls of the inlet hole 20 makes it possible to reduce the transfers of heat by conduction between parts 14 and 15 of the protective shell 12. During operation, part 15 is at a higher temperature than part 14, owing to the heat that it receives from the turbine casing 2. It is therefore desirable to reduce the transfers of heat between this part 15 and part 14, in order to improve the performance of the turbocharger. Instead of a space between the distal portion 18 of part 14 and the walls of the inlet hole 20 of part 15, it is also possible to use a thermally insulating material in order to reduce the thermal transfers between the two parts 14 and 15. Moreover, at least one of parts 14 and 15 is advantageously made, at least in part, using a material which helps reduce the transfers of heat by radiation, typically infrared, between the turbine casing 2 and the compressor casing 1. Indeed, the presence of a material of this kind having an advantageous level of opaqueness to radiation, typically infrared, makes it possible to further improve the performance of the turbocharger used in combination with the protective shell 12, since the transfers of heat between the turbine casing 2 and the compressor casing 1 are further reduced by its presence. 

1. A turbocharger comprising a compressor and a compressor casing (1) that encloses said compressor, a turbine and a turbine casing (2) that encloses said turbine, said compressor casing (1) comprising an inlet and an outlet for the air (4) admitted to a combustion chamber of an engine, said turbine casing (2) comprising an inlet and an outlet for the exhaust gases (5), a shaft (3) connecting said turbine and said compressor, at least one bearing (9 a, 9 b) for supporting and guiding in rotation said shaft (3), said turbocharger comprising means (6, 7 a, 7 b) for securing the compressor casing (1) to the turbine casing (2), characterized in that said shaft (3) comprises a free portion (8) between the two casings (1, 2), said securing means (6, 7 a, 7 b) being suitable for permitting the passage of a flow of air flowing along said free portion (8) and around said compressor casing (1) and turbine casing (2).
 2. The turbocharger as claimed in claim 1, in which the free portion (8) of the shaft (3) comprises air deflection means (10), said air deflection means (10) being suitable for generating a flow of air when said shaft (3) is rotating.
 3. The turbocharger as claimed in claim 2, in which the air deflection means (10) are suitable for generating a flow of air flowing in the direction from the compressor casing (1) to the turbine casing (2).
 4. The turbocharger as claimed in claim 2, in which the air deflection means comprise blades (10) attached to said shaft (3).
 5. The turbocharger as claimed in claim 1, in which a protective shell (12) is secured around said compressor casing (1), said turbine casing (2) and said free portion (8) of the shaft (3).
 6. The turbocharger as claimed in claim 1, in which the means for securing the compressor casing (1) to the turbine casing (2) comprise a plurality of bars (6).
 7. The turbocharger as claimed in claim 1, comprising a first bearing housing (9 a) located between the compressor casing (1) and the free portion (8) of the shaft, and a second bearing housing (9 b) located between the turbine casing (2) and the free portion of the shaft (8).
 8. A vehicle, characterized in that it comprises an internal combustion engine connected to a turbocharger as claimed in claim
 1. 